1. Field of the Invention
The present invention relates to a chemical vapor phase (CVP) method of forming gate insulating films such as passiviation film and reflection checking film, through formation of a nonoxide film or oxide film that includes halogen by thin film formation methods of cleaning the semiconductor surface by photochemical reactions and by a combined method of this method and a film formation process that utilizes photochemical reactions, without damaging the semiconductor surface by plasmas.
2. Description of the Prior Art
As a thin film formation method by vapor phase reaction, there is a known photo CVD method which activates the reactive gases by optical energy. The method has an advantage in that it enables film formation at low temperatures and that it does not damage the formed surface.
However, such photo CVD method is aimed simply at carrying out film formation, with none of the attempts to clean the semiconductor film surface prior to the formation of a film, by utilizing atoms, for example, of fluorine or chlorine, that are in excited states activated by light.
On the other hand, there is known the plasma CVD method that permits the formation of a thick film with thickness of 5,000 .ANG. to 1 micron, but it is also known to damage the substrate in the formation.
For this reason, for semiconductor devices, especially those in which the semiconductors themselves are extremely soft and vulnerable, made of such materials as the III-V group compounds, it has been attempted to generate active hydrogens by plasma to utilize them for cleaning the semiconductor surface. However, these active hydrogens have a large kinetic energy so that damages to the formed surface is inevitable. For this reason, it was not possible to apply the plasma cleaning method to the III-V group compounds.
In applying the photo CVD method, it makes use of a substrate (1) held within a reaction chamber (2), heating means (3) of the substrate, and a low pressure mercury lamp (9) for irradiating the substrate, as shown by an example illustrated in FIG. 1. A doping system (7) is equipped with a mercury bubbler (13) for exciting the reactive gas, and an exhaust system (8) is equipped with a rotary pump (19). In forming amorphones silicon, for example, on the substrate (which is at the tempertature of 250.degree. C. as a reaction product, through introduction of a reaction gas, for instance, disilane, from the doping system to the reaction chamber (2), these is also formed at the same time a thick silicon film on the covering plate (10), typically a quartz window, for transmission of ultraviolet rays that is provided in the reaction chamber. To prevent the formation of a film on the window, oil (an example of fluorine-based oils) (16) is thinly coated on the window.
Now, while the use of the oil prevents the formation of a silicon film on the window (10), it causes the mixing of the oil component in the film as an impurity. Further, the oil becomes easier to be mixed in the film when the distance between the window and the surface of the formed film is made small so that the distance cannot be made less than 4 cm (generally, it may be reduced only to 5 cm). On the other hand, however, reduction of the distance is effective for bringing more of ultraviolet rays (photon number) of 185 nm to the surface formed.